1. Field of the Invention
The present invention relates to a blanket-mounting mechanism for mounting a blanket onto a blanket cylinder of an offset press, as well as to a blanket.
2. Description of the Related Art
Conventionally, by means of a blanket-mounting mechanism, a blanket is mounted onto a blanket cylinder in the following manner. One end of the blanket is appropriately attached to the blanket cylinder. The blanket is wound onto the outer circumferential surface of the blanket cylinder. The other end of the blanket is inserted into a groove formed in a single dragging shaft disposed within the blanket cylinder. The dragging shaft is rotated so as to windingly drag the blanket into the blanket cylinder, thereby mounting the blanket onto the blanket cylinder. Such a blanket-mounting mechanism and a blanket are disclosed in, for example, Japanese Utility Model Application Laid-Open (kokai) No. 61-133332 and Japanese Patent Application Laid-Open (kokai) No. 7-285214.
The blanket-mounting mechanism disclosed in Japanese Utility Model Application Laid-Open No. 61-133332 includes a hollow dragging shaft, a torsion bar, and an adjustment mechanism. The dragging shaft is disposed in a groove which extends axially in the blanket cylinder and opens at the circumferential surface of the blanket cylinder. The opposite ends of the dragging shaft are rotatably supported by the opposite end portions of the blanket cylinder. The torsion bar is coaxially disposed within a hollow portion of the dragging shaft. One end of the torsion bar is connected to one end of the dragging shaft. The other end of the torsion bar projects from the other end of the dragging shaft. Via the adjustment mechanism, the projecting end of the torsion bar is attached to the corresponding end portion of the blanket cylinder, which end portion rotatably supports the other end of the dragging shaft. The adjustment mechanism is adapted to adjust the angular displacement of the torsion bar.
One end of the dragging shaft projects from the corresponding end portion of the blanket cylinder, which end portion rotatably supports the one end of the dragging shaft. A worm wheel is attached to the projecting end of the dragging shaft. A removable handled worm can be engaged with the worm wheel.
The blanket is mounted onto the blanket cylinder in the following manner. One end of the blanket is fixedly fitted into a groove which is axially formed in the circumferential surface of the blanket cylinder. The blanket cylinder is rotated so as to wind the blanket onto the outer circumferential surface of the blanket cylinder. The handled worm is set in a predetermined position so as to be engaged with the worm wheel and is rotated manually to thereby rotate the worm wheel. As the worm wheel rotates, the dragging shaft rotates to thereby twist the torsion bar, since one end of the torsion bar is connected to the dragging shaft. Thus, a restoration force is accumulated. When a blanket attachment portion of the dragging shaft reaches an appropriate position through rotation of the dragging shaft, the other end of the blanket is attached to the blanket attachment portion.
Next, the handled worm is rotated in the reverse direction so that the dragging shaft windingly drags in the other end of the blanket. When the tension exerted by the blanket and the restoration force accumulated in the torsion bar balance with each other, the worm wheel stops rotating. When the handled worm is rotated further in the reverse direction, the handled worm is disengaged from the halted worm wheel.
Thus, mounting of the blanket onto the blanket cylinder is completed.
In the blanket-mounting mechanism disclosed in Japanese Patent Application Laid-Open No. 7-285214, the opposite ends of a dragging shaft project from the corresponding end faces of a blanket cylinder. Rotating means composed of a worm and a worm wheel is disposed at each end of the dragging shaft.
Further, Japanese Patent Application Laid-Open No. 7-285214 states that some blanket-mounting mechanisms employ a structure in which rotating means comprising a lever and a latch mechanism is provided. The publication also discloses a structure such that a blanket to be attached to a blanket cylinder is provided with a thin band sheet attached to opposite end portions of the blanket cylinder to be located on a single side thereof.
The above-mentioned conventional techniques involve the following problems.
In the blanket-mounting mechanism disclosed in Utility Model Application Laid-Open (kokai) No. 133332/1986, a torque exerted by the torsion bar is transmitted to the dragging shaft through one end thereof to thereby rotate the dragging shaft. The blanket is windingly dragged into the blanket cylinder and is thus wound onto the blanket.
However, in the case of a long dragging shaft, the other end of the dragging shaft to which a torque exerted by the torsion bar is not directly transmitted exhibits a smaller angular displacement than does the opposite end, because of the action of a frictional force. As a result, the dragging shaft is twisted.
Since a central portion of the dragging shaft is not supported, the dragging shaft deflects at the central portion due to the tension exerted by the blanket.
Thus, the blanket mounted on the blanket cylinder is not subjected to uniform tension. The blanket is mounted on the blanket cylinder while being pulled at a constant tension and remaining in close contact with the surface of the blanket cylinder. Since the blanket is stretched, the thickness thereof varies slightly.
Moreover, if a nonuniform tension is exerted on the blanket, the thickness of the blanket becomes nonuniform, causing nonuniform contact pressure between the blanket and a printing cylinder or between the blanket and printing paper. As a result, a certain portion may not be printed under an appropriate pressure, with a resultant impairment in printing quality.
In the blanket-mounting mechanism disclosed in Japanese Patent Application Laid-Open No. 7-285214, when the blanket is to be windingly dragged into the blanket cylinder, the opposite ends of the dragging shaft must be alternatingly rotated. Dragging work is both labor consuming and time consuming.
In the case of the rotating means composed of a lever and a latch mechanism, one end of the dragging shaft is rotated so as to windingly drag the blanket into the blanket cylinder, and then the other end of the dragging shaft is rotated so as to compensate a torsion of the dragging shaft. Since the angular displacement of the dragging shaft, or the degree of drag of the blanket, and the reverse angular displacement of the dragging shaft for compensation of a torsion of the dragging shaft are in units directly related to the tooth pitch of the latch mechanism, the tension exerted by the mounted blanket cannot be adjusted optimally for the thickness and physical characteristics of the blanket.
As a result, the tension exerted by the blanket mounted on the blanket cylinder may be slightly weak or strong with respect to an optimum level, resulting in a failure to obtain desired printing quality. Also, the life of the blanket is shortened.
Further, since the deflection of the dragging shaft cannot be prevented, the blanket cannot be mounted onto the blanket cylinder while being subjected to uniform tension. Therefore, as in the case of the blanket-mounting mechanism disclosed in Utility Model Application Laid-Open No. 61-133332, good printing quality is not provided.
The blanket disclosed in Japanese Patent Application Laid-Open No. 7-285214 has a band sheet attached to opposite end portions located on a single side. The band sheet serves as a reinforcing member and is long and narrow. When a worker handles the band sheet, an external force may be exerted thereon, potentially causing a slight warpage or torsion thereof. Particularly, in the case of a deformation of the band sheet to be attached to an end portion of the blanket which is to be inserted into a groove formed in the dragging shaft, insertion of the end portion into the groove may become difficult or impossible.
An object of the present invention is to provide a blanket-mounting mechanism featuring a simple mechanism and easy operation, allowing a blanket to be easily mounted onto a blanket cylinder, capable of adequately adjusting the tension exerted by the mounted blanket so as to optimize the state of drag according to the thickness and physical properties of the blanket, and capable of adequately compensating a torsion of a dragging shaft to thereby enable of mounting of the blanket with uniform tension.
Another object of the present invention is to provide a blanket-mounting mechanism capable of minimizing the deflection of the dragging shaft due to the tension exerted by the blanket to thereby enable of mounting of the blanket with more uniform tension.
Still another object of the present invention is to provide a blanket in which a reinforcing member attached to one end thereof to be inserted into a groove formed in the dragging shaft is not susceptible to deformation.
To achieve the above objects, the present invention provides a blanket-mounting mechanism comprising a blanket cylinder having a dragging-shaft accommodation bore and a blanket insertion groove, a dragging shaft, rotating means, and correction means. The dragging-shaft accommodation bore extends axially through the blanket cylinder. The blanket insertion groove extends axially on the outer circumferential surface of the blanket cylinder and extends radially to the dragging-shaft accommodation bore. The dragging shaft has a blanket-end reception groove formed on the outer circumferential surface. The blanket-end reception groove has an appropriate width and depth so as to receive one end of a blanket to be mounted on the blanket cylinder. The dragging shaft is inserted into the dragging-shaft accommodation bore with an appropriate gap maintained therebetween. The opposite end portions of the dragging shaft are rotatably supported by and project from the corresponding end faces of the blanket cylinder. The rotating means is disposed at the side of one end face of the blanket cylinder and is connected to the corresponding end portion of the dragging shaft so as to rotate the dragging shaft. The correction means is disposed at the side of the other end face of the blanket cylinder and comprises an angular-displacement member and adjusting means. The angular-displacement member is attached to the corresponding end portion of the dragging shaft in such a manner as to be able to grip/release the end portion of the dragging shaft. The adjusting means angularly displaces and positions the angular-displacement member about the dragging shaft.
Preferably, one of two side walls that define the blanket insertion groove is substantially in parallel to a plane tangent to the dragging-shaft accommodation bore, and the other side wall extends in a radial direction of the blanket cylinder and toward the center of the dragging-shaft accommodation bore. Thus, the blanket insertion groove assumes a wedged cross section that tapers down toward the outer circumferential surface of the blanket cylinder.
Preferably, the blanket-mounting mechanism further comprises deflection suppression means disposed in the blanket cylinder in at least one axial position. The deflection suppression means faces the circumferential surface of the dragging shaft accommodated within the dragging-shaft accommodation bore with a small gap formed therebetween. The deflection suppression means rotatably supports the dragging shaft while restricting deflection of the dragging shaft to an amount corresponding to the small gap.
Preferably, the deflection suppression means is a block fitted in a depression formed in the blanket cylinder. The block has a cylindrically curved inner surface which is concentric with the dragging-shaft accommodation bore, which has a diameter smaller than that of the dragging-shaft accommodation bore, and which faces the circumferential surface of the dragging shaft with a small gap formed therebetween so that the block can rotatably support the dragging shaft while restricting deflection of the dragging shaft to an amount corresponding to the small gap.
The present invention further provides a blanket to be mounted on a blanket cylinder. The blanket comprises a blanket body and two band sheets serving as reinforcing members and attached to the corresponding parallel, opposite end portions of the blanket body across the width of the end portions. One of the band sheets is attached to one end portion of the blanket body and on the side of the blanket body which comes into contact with the blanket cylinder when the blanket is mounted on the blanket cylinder. The other band sheet is longitudinally folded in two and is attached to the other end portion of the-blanket body such that the other end portion is sandwiched therebetween.
The above-mentioned blanket is mounted on the blanket cylinder in the following manner. The dragging shaft is released beforehand from the angular-displacement member of the correction means. The angular-displacement member is rotated about the dragging shaft to an appropriate angular position.
The dragging shaft must be in such an angular position that the blanket-end insertion groove formed therein is aligned with the blanket insertion groove formed in the blanket cylinder. If the dragging shaft is not in such a position, the dragging shaft is rotated thereto by use of the rotating means.
One end portion of the blanket is inserted into the blanket insertion groove such that the band sheet attached to the blanket end portion faces the side wall of the blanket insertion groove.
Upon starting of a printing press, the blanket cylinder is rotated at low speed. The blanket begins to be wound onto the circumferential surface of the blanket cylinder. Upon completion of about one rotation, the blanket cylinder is caused to stop rotating. The blanket is wound on the blanket cylinder.
The other end portion of the blanket is inserted into the blanket insertion groove along the side wall of the groove until the band sheet of the other end portion of the blanket is fitted into the blanket-end reception groove formed in the dragging shaft.
The dragging shaft is rotated by use of the rotating means so as to windingly drag in the blanket. As the tension exerted by the blanket increases, the end portion of the blanket located within the blanket insertion groove is pressed further toward a side wall of the blanket insertion groove by a portion of the blanket which is being dragged in, thereby being fixed within the blanket insertion groove. The end portion is only slightly susceptible to deformation by virtue of the band sheet attached thereto as a reinforcing member.
As the dragging shaft is rotated further to further drag in the blanket, the tension exerted by the blanket increases further, causing a deflection of an axially central portion of the dragging shaft. However, the deflected portion of the dragging shaft comes into contact with the inner curved surface of the block serving as the deflection suppression means and disposed in the direction of deflection of the dragging shaft, thereby preventing a further deflection of the dragging shaft and thus maintaining constant the tension exerted by the blanket mounted on the blanket cylinder.
As mentioned above, the blanket is wound onto the blanket cylinder by use of the rotating means. The angular displacement of one end portion of the dragging shaft which is directly rotated by the rotating means is greater than that of the other end portion of the dragging shaft which is rotated as a follower, causing a torsion of the dragging shaft. As a result, the tension exerted by the blanket becomes nonuniform.
In order to compensate the nonuniform tension exerted by the blanket, the angular-displacement member of the correction means is caused to grip the end portion of the dragging shaft. The angular-displacement member is rotated about the axis of the dragging shaft so as to compensate an insufficient angular displacement of the gripped end portion of the dragging shaft with respect to the angular displacement of the directly rotated end portion of the dragging shaft. The gripped end portion of the dragging shaft is rotated accordingly.
Thus, the torsion of the dragging shaft is eliminated, thereby compensating the difference in the tension exerted by the blanket as observed between the opposite end portions of the dragging shaft. The blanket is mounted on the blanket cylinder while being subjected to uniform tension.
The blanket-mounting mechanism according to the present invention facilitates the operation of mounting the blanket onto the blanket cylinder, prevents deflection of the dragging shaft, which would otherwise occur during the mounting operation, and corrects and eliminates torsion of the dragging shaft.
Accordingly, the blanket can be attached to the blanket cylinder with uniform tension, so that high printing quality is guaranteed.
Further, at one end of the blanket which is inserted into the blanket-end reception groove of the dragging shaft via the blanket insertion groove of the blanket cylinder, one band sheet is attached to a surface of the blanket body which comes into contact with the blanket cylinder when the blanket is mounted on the blanket cylinder. Another band sheet is longitudinally folded in two and is attached to the other end portion of the blanket body such that the other end portion is sandwiched therebetween. The thus-attached band sheets reinforce the corresponding end portions of the blanket to thereby prevent warpage or torsion which the blanket end portions would otherwise undergo during mounting of the blanket onto the blanket cylinder.
Accordingly, during mounting of the blanket onto the blanket cylinder, a worker can easily and reliably insert one end portion of the blanket into the blanket-insertion groove formed in the blanket cylinder and the other end portion of the blanket into the blanket-end reception groove formed in the dragging shaft. Thus, the burden imposed on the worker is reduced, and work efficiency is improved.